The invention is directed to an apparatus for electrical function testing of wiring matrices, particularly of printed circuit boards. The apparatus has a carrier plate that can be placed onto the wiring matrices and in which a plurality of contact elements are arranged, whereby respectively at least two selected measuring points of a wiring matrix can be contacted via the allocated contact elements.
In automatic testing units and test adapters for unequipped and equipped printed circuit boards as well as for wiring matrices using solder or crimp technology, the contacting of the selected measuring locations is usually undertaken via resilient test probes. The resilient test probes arranged according to a dimensioned grid of a wiring matrix to be tested are secured with spring sleeves that are pressed into a carrier plate and into which the test probes are inserted (Elektronik Produktion und Preuftechnik, November 1979, pages 472 and 473).
Given the use of resilient test probes as contact elements, increasing difficulties arise in view of the decreasing grid dimension and increasing area of the printed circuit boards. Thus, an arrangement of the resilient test probes in grid dimensions below one millimeter can hardly be achieved in terms of precision mechanical structure to give a reliable contacting of the measuring locations. The number of required leads and switch elements also increases with the plurality of measuring locations that, for example, can amount to a hundred thousand, thereby requiring a considerable appatarus-oriented outlay and correspondingly high costs.
EP-A-No. 0 102 565 discloses an apparatus for electrical function testing of wiring matrices wherein the hitherto standard, ohmic contacting of the measuring locations, is replaced by a non-touching, ionic contacting via gas discharge paths. To this end, a plurality of gas discharge channels provided with electrodes are introduced into the carrier plate that can be placed onto the wiring matrices. The gas discharge channels, arranged in the grid of the wiring matrixes, are open toward the measuring locations. When two, selected measuring locations are connected to one another in electrically conductive fashion by, for example, an interconnect, then the allocated gas discharge channels form two gas discharge paths connected in series that can be ignited by applying an adequately high voltage to the electrodes. A current flow that can be analyzed for testing purposes then occurs with the ignition of the gas discharges. When the ignition of the gas discharges does not occur or when too low a current flows after an ignition, then conclusions regarding an interrupt, electrically conductive connection or regarding an electrically conductive connection that did not exist from the very beginning between the selected measuring locations can be determined. When an alternating voltage is superimposed on the voltage applied to the electrodes, then the current change resulting therefrom can be measured phase-sensitive relative to the applied alternating voltage and can be utilized for identifying the resistance of a connection existing between the selected measuring locations.
The known apparatus thus enables conductivity and insulation measurements, whereby an extremely high reliability is achieved by avoiding ohmic contacts. In particular, wiring matrices having small grid dimensions of the measuring locations down to 0.1 mm can then be reliably tested by the principle of ionic contacting of the measuring locations via gas discharge channels realizable in extremely small dimensions. Given the great number of measuring locations in a wiring matrix to be tested, however, those same problems that can be attributed to the numerous leads and switch elements for the connection of the electrodes of the gas discharge channels continue to exist.